watchdog: imx2_wdg: suspend watchdog in WAIT mode

Putting device into the "Suspend-To-Idle" mode causes watchdog to
trigger and resets the board after set watchdog timeout period elapses.

Introduce new device-tree property "fsl,suspend-in-wait" which suspends
watchdog in WAIT mode. This is done by setting WDW bit in WCR
(Watchdog Control Register). Watchdog operation is restored after
exiting WAIT mode as expected. WAIT mode corresponds with Linux's
"Suspend-To-Idle".

Signed-off-by: Andrej Picej <andrej.picej@norik.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20221104070358.426657-2-andrej.picej@norik.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>